1. Field of the Invention
The present invention relates to    (1) a polymeric sulfonium salt as an acid generator,    (2) a resist composition comprising (1), used in exposure to high energy beam, preferably with a wavelength of 300 nm or 200 nm or less, especially to ArF excimer laser, F2 excimer laser, EUV, X-ray or EB, and    (3) a patterning process using this resist composition.
2. Description of the Related Art
In recent years, higher integration and higher speed of LSI have been developed, and finer pattern rule has been demanded. Then, Deep-ultraviolet lithography and vacuum ultraviolet lithography are regarded as possible micropatterning technique of next generation. Especially, photolithography using ArF excimer laser light as a light source is an indispensable technique for ultra micropatterning of 0.13 μm or less.
In the photolithography using ArF excimer laser light as a light source, in order to prevent deterioration of delicate and expensive optical equipment, a resist composition with high sensitivity that realizes sufficient resolution with low exposure dose has been demanded. The most common way to realize such a resist composition with high sensitivity is to select respective constituents that has high transparency at the wavelength of 193 nm. For example, as for a base resin, polyacrylic acid and derivatives thereof, norbornene-maleic anhydride alternating copolymer, polynorbornene, metathesis ring-opening polymer, etc. are suggested. And the suggestion has achieved some results in respect to increasing transparency of a resin itself.
ArF lithography has begun to be used partially since device fabrication at 130 nm node, and has become the main lithography technique since 90 nm node device. 157 nm lithography using F2 laser was originally regarded as possible lithography technique of next 45 nm node. However, delay of development was pointed out due to problems like the quality of a CaF2 single crystal used for a projection lens, design change of optical system owing to indispensable use of hard pellicle, and deterioration of etch resistance of a resist. Therefore, the ArF liquid immersion lithography has suddenly gathered attention (for example, see Journal of photopolymer Science and Technology Vol. 17, No. 4, p587 (2004)).
The more numerical aperture (NA) of a projection lens projecting image of pattern onto a substrate grows, the more resolution thereof increases. In the liquid immersion lithography, a gap between a projection lens and a wafer is filled with a liquid with a higher index of refraction than that of air to design NA of the projection lens to be 1.0 or more, thus high resolution can be achieved. As for the liquid, water with an index of refraction of 1.4366 has been under review.
However, there are problems that resist pattern obtained through the liquid immersion exposure and development is collapsed or becomes T-top profile. Therefore, a patterning process that can obtain an excellent resist pattern after development in the liquid immersion lithography has been demanded.